The concentration of burnable neutron absorbers such as Gd.sub.2 O.sub.3 in nuclear reactor fuels is a factor in determining core reactivity during reactor operation after fuel insertion into the core. Prediction of core reactivity is a safety parameter and it is also useful in efforts to optimize reactor performance and to minimize waste.
A conventional method of determining gadolinia content involves destructive testing. This involves essentially testing in a chemical laboratory. Unfortunately, this consumes a portion of the fuel examined. Furthermore, such tests are not capable of being performed "on site" where the fuel is actually manufactured, but necessitates moving fuel specimen to the laboratory itself, causing substantial time delays.
As performed by the instant invention, a non-destructive analysis is performed by x-ray fluorescence which, as is known to those familiar with the art, can be used to measure the concentrations of one or more secondary materials or elements in suitable matrices of elements of a primary material using methods such as those described in standard references such as X-Ray Absorption and Emission in Analytical Chemistry by H. A. Liebhafsky, H. G. Pfeiffer, E. H. Winslow, and P. D. Zemany (John Wiley & Sons, New York, 1960); Practical X-Ray Spectrometry by R. Jenkins and J. L. DeVries (Springer-Verlag, New York, 1967); X-Ray Spectrochemical Analysis, second edition, by L. S. Birks (Interscience, New York, 1969); and Principles and Practice of X-Ray Spectrometric Analysis by E. P. Bertin (Plenum Press, New York, 1970). In the instant invention, specimens are irradiated with primary radiation and secondary radiation of the elements of interest is detected and measured. In one embodiment, the secondary radiation response includes x-rays from K-band gadolinium electrons and L-band uranium electrons.
The secondary radiation varies as a result of environmental, including thermal, factors. Insofar as the x-ray response and counts are commonly affected, the common influence of environmental variations can be factored out by obtaining ratios of radiation from secondary materials including for example gadolinium to that of a primary material such as for example uranium, and determining concentrations of these secondary materials or elements from pre-established calibration curves according to the instant invention.